A vertical type furnace may be employed to perform a semiconductor manufacturing process such as a diffusion process and a chemical vapor deposition (CVD) process.
The vertical type furnace heats up an interior thereof and supplies a reaction gas thereto, to thereby form a thin film on a surface of a substrate to be processed such as a wafer or the like. The vertical type furnace is provided with a heater for this purpose.
With reference to FIG. 8, a vertical type furnace having a conventional heater for use in a semiconductor manufacturing apparatus will be described.
A vertical type furnace 1 is provided with a cylindrical type heater 2. A uniform heating tube 3 and a reaction tube 4 are concentrically disposed in an interior of the heater 2. A boat 5 is inserted into and disposed in the reaction tube 4. The boat 5 is placed over an elevator cap 7 through a boat cap 6. The elevator cap 7 is configured to be movable upward and downward by a boat elevator (not shown).
A gas introduction conduit 8 is inserted into and communicated with an upper portion of the reaction tube 4. An exhaust port 9 is disposed on a lower portion of the reaction tube 4. A lower portion of the gas introduction conduit 8 is connected to a gas supply conduit 10. The exhaust port 9 is connected to an exhaust conduit 11.
The boat 5 may be discharged from the reaction tube 4 and a predetermined number of sheets of wafers 12 may be loaded on the boat 5. Thereafter, the boat 5 loading the wafers 12 thereon may be moved upward by the boat elevator (not shown) to be inserted into and disposed in the reaction tube 4. The heater 2 then may heat up an interior of the reaction tube 4 to a predetermined temperature. A reaction gas may be introduced into the reaction tube 4 through the gas supply conduit 10 and the gas introduction conduit 8. As a result, a thin film may be formed on a surface of the respective wafers 12. The reaction gas remaining after the thin film formation may be exhausted through the exhaust port 9 and the exhaust conduit 11.
Hereinafter, with reference to FIG. 9, FIG. 10A and FIG. 10B, the conventional heater 2 will be described in detail.
FIG. 9 is a schematic vertical cross-section view of the conventional heater 2. The heater 2 includes a coil type heating element 13 configured to enclose the surroundings of the uniform heating tube 3 (not shown in FIG. 9), support pieces 14 configured to support the heating element 13, a piece holder 15 configured to hold the support pieces 14, a periphery heat insulator 16 provided to be wound around the piece holder 15, and a ceiling heat insulator 17 configured to seal a ceiling portion of the periphery heat insulator 16. The periphery heat insulator 16 and the ceiling heat insulator 17 are enclosed with a heater case (not shown). The heating element 13 has a circular cross-section and is supported at positions, which are equally spaced by the support pieces 14 on a circumference of the heater 2.
The support pieces 14 may be made of high alumina material. A multiple number of the support pieces 14 may be vertically connected to each other. FIG. 10A and FIG. 10B are a plan view and a front view of the support piece, respectively. On an upper surface of each of the support pieces 14, protrusions 18 and 19 are formed to diagonally extend in an upper outer direction. An upward-facing curved concave surface 21 of a semicircular cross-section is formed to connect the protrusions 18 and 19 to each other. Also, on a lower surface of each of the support pieces 14, a concave portion 22 is fainted to have a concave insertion 23 having a reverse-trapezoid cross-section and a downward-facing concave curved surface 24 having a semicircular cross-section, which is consecutively coupled to the concave insertion 23. The concave insertion 23 of one support piece is configured so that the protrusions 18 and 19 of another support piece can be insert-fitted thereto (or engaged therewith). By insert-fitting the protrusions 18 and 19 to the concave insertion 23, a hollow is formed by a combination of the upward-facing curved concave surface 21 and the downward-facing curved concave surface 24, such that the heating element 13 may be inserted into the hollow.
FIG. 11A and FIG. 11B show a plan view and a front view of another example of the conventional support piece, respectively.
A convex insertion 26 having a reverse-trapezoid cross-section is formed on an upper left side of a support piece 25. Both lateral ends of the convex insertion 26 are diagonally extended from the upper side of the support piece 25 in an upper outer direction. Also, on a right side from the convex insertion 26, an upward-facing curved concave surface 27 having a semi-elliptical cross-section is formed. Further, on a lower left side of the support piece 25, a concave insertion 28 having a reverse-trapezoid cross-section is formed. The concave insertion 28 of one support piece is configured so that the convex insertion 26 of another support piece may be insert-fitted thereto. By insert-fitting the convex insertion 26 to the concave insertion 28, a hollow is formed by a combination of the upward-facing curved concave surface 27 and a lower surface of the support piece 25, such that the heating element 13 may be inserted to the hollow.
In the conventional heater 2, an external force may be applied to the multiple-connected support pieces 14 or 25, e.g., due to vibration of the heating element 13 during transportation or thermal expansion/contraction of the heating element 13 during a film forming process performed on the wafer 12. In this case, the external force may be concentrated on one of the multiple-connected support pieces 14 or 25 in a radial or circumferential direction. Specifically, when using the support piece 14, stress (or external force) may be concentrated on an angled portion of the concave insertion 23 of the support piece 14 as shown in FIG. 12A. On the other hand, when using the support piece 25, stress may be concentrated on an angled portion of the concave insertion 28 of the support piece 25 as shown in FIG. 13A. That is, the stress may be concentrated on the vicinity of a portion where the support pieces 14 or 25 are connected to each other, and thus damage may occur at the connection portion of the support pieces 14 or 25. The damage of the support piece 14 or 25 may diminish the heating efficiency of the heater 2.
Further, if some fragments are separated and fall from the damaged support piece 14 or 25, this may cause the multiple-connected support pieces 14 or 25 to be unable to securely support the heating element 13. This in turn may cause a short circuit between different portions of the heating element 13 due to an electrical coupling thereof. Also, the heating element 13 may contact the uniform heat tube 3, which may cause an accident such as electric leakage. As a result, the expected lifespan of the heating element 13 may be reduced.
Further, in the conventional heater 2, as shown in FIG. 14, e.g., due to vibration generated during transport or due to thermal expansion/contraction of the heating element 13, the multiple-connected support pieces 14 or 25 and the piece holder 15 may be separated from the periphery heat insulator 16. Furthermore, the ceiling heat insulator 17 may be separated from the periphery heat insulator 16 due to a thermal expansion difference between the piece holder 15 and the periphery heat insulator 16. As a result, a gap may be formed between the ceiling heat insulator 17 and the periphery heat insulator 16, which causes heat leakage through the gap and deteriorates the adiabatic efficiency.
In order to overcome the above problems, a heater supporting device has been proposed for preventing support pieces from being misaligned or damaged due to thermal expansion/contraction of a heating element, by limiting relative displacements of the respective support pieces in radial and circumferential directions of a vertical type furnace, and also limiting the movement of a piece holder connected to the respective support pieces in a centric direction of the vertical type furnace (for example, See Japanese Laid-Open Patent Publication No. Hei-11-67424).